Baffle arrangement for chemical recovery boiler



J. H. FREIDAY 2,994,287 BAFFLE ARRANGEMENT FOR CHEMICAL RECOVERY BOILER Aug. 1, 1961 Filed Dec. 10, 1958 INVENTOR JAY H. FRE/DAY BY (w A. Z0212 ATTORNEY United States Patent 2,994,287 BAFFLE ARRANGEMENT FOR CHEMICAL RECOVERY BOILER Jay H. Freiday, Chatham, N.J., assignor to Combustion Engineering, Inc., New York, N.Y., a corporation of Delaware Filed Dec. 10, 1958, Ser. No. 77 9,333 1 Claim. (Cl. 110-98) This invention relates to tubular heat exchangers and has particular relation to such heat exchangers comprised of vertical tube bundles having baflles disposed to direct a gas back and forth across the bundles.

It is well established that a greater heat transfer is generally had by directing a stream of gases that forms a heating or cooling medium transversely across a bundle of heat exchange tubes rather than in parallel relation with these tubes and it has long been the practice to employ bafiles in order to obtain this cross flow effect with the bafiles directing the gas stream sinuously of or back and forth across a tube bundle through the tubes of which there flows a fluid that is to be heated or cooled. One of the difiiculties that has been experienced in certain heat exchange apparatus, when the tube bundle is comprised of vertically disposed tubes, is that the baflles do not have sufiicient slope to make the removal of material deposits thereon an uncomplicated and simple task but rather have such a low degree of slope that the material collects on the bafiles with it being very difficult to remove the same. 'One such heat exchange organization wherein this particular problem prevails is 'in the boilers that are employed in so-called chemical recovery units which use as their fuel a residual liquor obtained in the chemical digestion process of cellulose bearing material in the manufacture of pulp. The reason for the low degree of incline of these bafiles is that if the incline were increased suficiently to alleviate the problem a satisfactory transverse flow of the hot gases across the tubes would not be had and the openings between adjacent bafiles would be restricted to a point that could not be tolerated. While the invention has application to other heat exchange organization, it is particularly well adapted for use with the furnaces of chemical recovery boilers, for the reason that there is a serious problem with regard to the collection of foreign material on the bafiles in these boilers as it is a characteristic of these boilers that the heating gases contain substantial amounts of foreign material because of the type of fuel that is employed and, moreover, these boilers are so arranged that vertical tube bundles in relatively narrow passages are utilized.

The present invention overcomes or alleviates to a substantial extent the difliculty experienced with bafiles as hereinbefore mentioned. In accordance with the invention the baffle means employed to direct the heating gas back and forth across the vertically disposed tube bundles comprises a plurality of bafile assemblies that are vertically spaced, with each of the assemblies being comprised of a plurality of separate rather short baffles disposed in horizontally spaced relation in the same generally vertical zone and inclined at an angle that is slightly greater than the angle of repose of the foreign material that is entrained in the heating gases. These relatively short baflles of each assembly are inclined in a direction such that notwithstanding that they are horizontally spaced they effectively direct the gas flow back and forth across the tube bundle.

It is an object of this invention to provide an improved organization employing a vertical tube bundle and having baflie means arranged to direct a gas back and forth across this tube bundle.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the invention comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawing wherein:

FIG. 1 is a diagrammatic representation in the nature of a vertical section through a boiler and a portion of the furnace of a chemical recovery unit; and

FIG. 2 is a transverse section of the economizer of this boiler and is taken generally along line 22 of FIG. 1.

Referring now to the drawings, wherein like reference characters are used throughout to designate like elements, the illustrative and preferred embodiment of the invention depicted therein comprises a chemical recovery furnace 10 into which liquor is introduced through a suitable nozzle 12 with combustion supporting air being introduced through the air inlets 14. The combustion gases that are generated by burning the liquor in furnace 10 pass up through the furnace and then through the boiler which is designated generally 16. Boiler 16 includes upper and lower drums 18 and 20, respectively, between which drums extends a large number of heat exchange or steam generating tubes 22 with these tubes being divided into two separate groups, in the illustrative organization, with one group being located in passageway 24 which is defined by bafiles 26 and 28 and with the other group being located in passageway 30 which is defined by battles 28 and 32. The combustion gases pass down through passageway 24, reverse their direction at the bottom of battle 28 and then pass up through passageway 30 with the inclined baflles 34 that extend laterally from bathe 28 being for the purpose of providing a somewhat turbulent flow of gases up through passageway 30 and for ensuring that the gases are directed over the tubes in this passageway.

Upon emerging from passageway 30 the gases are directed over the economizer of the boiler with this economizer being comprised of tube bundle 36 which is made up of a group of vertically disposed tubes 37 that extend between lower header 38 and upper header 40. This tube bundle is disposed in passageway 42 that is defined by baffle 32 and boiler wall 44 with the boiler wall forming the rear wall of the passageway 42 and baflle 32 forming the front wall thereof. Tubes 37 that make up tube bundle 42 are disposed in spaced relation and the tube bundle extends across substantially the entire width of passageway 42 as best shown in FIG. 2.

The hot combustion gases pass across the upper end of tube bundle 36 and then are directed downwardly and back and forth, in a tortuous path, across this tube bundle with these gases finally exiting through outlet 46 and with the gases being directed in this manner by means of suitable bafiling.

In accordance with the invention this baflling is comprised of the bafile assemblies 48, 50 and 52. The assembly 43 includes baflie plate or section 54 which is the upper end of baffle 32 inclined in the manner shown. In horizontally spaced relation but generally at the same vertical location as baflle plate 54 are the additional baffle plates 56 with these plates being relatively short in width, traversing or extending across much less than the full thickness or depth of the tube bundle, i.e., the dimension A, and being inclined from the horizontal in the direction of the gas flow so that they present a louvered effect and so the air passing thereover is, upon striking the same, directed upwardly into the space thereabove. These baflle plates are of a length such that they extend across the entire width of passageway 42 and the inclination of the baflle plates is slightly greater than the angle of repose of the foreign material that is carried along with the hot combustion gases that pass through the boiler. This inclination causes only a very minor amount of foreign material to collect on the baffle and renders the removal of this material a simple and easy task.

After passing over bafile assembly 48 the gases are directed down through the passage 58 between assembly 48 and the rear wall 44 of passage 42. The baffle assembly 50 is then effective to direct these gases back across the tube bundle 36 with this assembly being comprised of baffle plates 58 and baille plates 60 with the baffle plate 58 extending inwardly from wall 44 through about one third of the depth of the tube bundle 36 and with the bafile plates 60, which are in the nature of the previously mentioned baflle plates 56 of assembly 78, elfectively and collectively extending across the remainder of the depth of tube bundle 36 with these baffle plates 60 being horizon-tally spaced and at generally the same vertical location and being inclined with the horizontal in the direction of the combustion gas flow. Each of the baflie plates 58 and 60 is also inclined at an angle slightly greater than the angle of repose of the material entrained in the gas stream, and they are inclined with the horizontal in the direction of gas flow in a manner to direct the flow across the tube bundle as is indicated by arrows 61 which show gas flow.

The combustion gases pass around the end of bafile assembly 50 down through passageway 62 that is located between this bafile 70 and the front wall 32 of passage 42. The combustion gases are then directed by baflie assembly 52 back across tube bundle 36, through passage 64 located between this battle 62 and wall 44 and then again across tube bundle 36 and exit through outlet 46. Battle assembly 52 is comprised of adjustable damper 66, baffle plate 68 and baffle plate 70. Damper 66 and bafiie plate 68 together effectively form a bafile, when the damper is in the position shown, that extends downwardly from the vertically disposed front wall 32 with the separate and short baffles 70 being generally in the same vertical location and horizontally spaced and with the entire assembly 52 being similar to assembly 50 but extending from the opposite wall of passage 42. Each of the bafile plates 68 and 70 is inclined at an angle slightly greater than the angle of repose of the foreign material entrained in the combustion gases with this angle being generally about 50 in a chemical recovery unit.

The purpose of adjustable damper 66 is to regulate the heat input of the economizer and the temperature of the gases passing through outlet 46 with it being possible to have a large portion of the combustion gases pass directly from the location of bafie assembly 50 down through passage 62 to outlet 46 and accordingly by-pass the entire lower portion of the economizer. By suitably adjusting damper 66 between the position shown in FIG. 1 and the vertical position where the maximum by-pass efiect such that there are no baffles or bafile surfaces presented which are at an incline less than at the angle of repose of the material entrained in the combustion gas while at the same time the space or distance between vertically disposed bafile assemblies is not unduly restricted and a a satisfactory direction and passage of the gases transversely of the tube handle is provided.

hile I have illustrated and described a preferred embodiment of my invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

What I claim is:

In combination, a vertically disposed passageway of rectangular transverse configuration and through which a gas containing foreign matter is passed downwardly, said passageway having openings at its upper and lower ends for this purpose, a bundle of vertical heat exchange tubes in said passageway, bafile means eifective to cause said gas to travel a tortuous path through the passageway back and forth across the tube bundle, said baffie means comprising a plurality of baffle assemblies vertically spaced throughout the passageway with successive assemblies extending alternately from the front and rear walls of the passageway, extending entirely across the tube bundle in the direction of gas flow and terminating in spaced relation with the opposite wall thereby forming a tortuous path, each of said assemblies comprising a plurality of separate battles extending between the sides of the passageway, said separate bafiies having a width substantially less than the tube bundle and said separate bat-fies being in side by side closely horizontally spaced relation and inclined to the horizontal so as to provide a louvered effect in the direction of gas flow such that the gas is directed over the edges of the several baflles with this inclination being approximately but slightly greater than the angle of repose of the material, each of the assemblies downstream of the first assembly relative to gas flow including baffle means inclined at an angle greater than the angle of repose and positioned generally above and upstream of the baflles of these assemblies which produce the louvered efiect.

References Cited in the file of this patent UNITED STATES PATENTS 2,379,009 Kuhner June 26, 1945 2,415,068 Andrew Feb. 4, 1947 2,577,268 R-asanen Dec. 4, 1951 2,614,544 Patterson et -al. Oct. 21, 1952 2,762,201 Sampson Sept. 11, 1956 

